The present invention relates to treatment of green coffee beans for preparing them for extraction for obtaining a beverage.
Techniques for treating green coffee beans for preparing the beans for extraction to obtain a beverage include a step which conventionally involves roasting green beans by heating them with hot gases for driving off free and bound water from the beans. This heating initiates and provides for a reaction known as pyrolysis which is essential for developing aromatic, flavor and color characteristics associated with roast and ground coffee. If the roasting conditions are not controlled appropriately, however, charring, or burning, of the coffee beans can occur which produces beans having undesirable aromatic and flavor characteristics. Upon extraction with water utilizing apparatus available to the consuming public, a yield of soluble coffee solids in the extraction brew which is on the order of from about 20% to about 25% by weight based upon the weight of the roasted beans is obtained.
As higher brew yields have been desired, various methods have been proposed to increase the yield of coffees to be extracted for the preparation of a beverage which include subjecting coffee beans to a hydrolysis reaction.
Additionally, it is well accepted that certain varieties of coffees provide extracts which have characteristics which limit their usefulness. Such varieties include "Robustas", for example, which when roasted with heated gases provide extracts which are commonly described as "earthy", "woody" and/or "rubbery", for example. More importantly, such coffees are characterized as being "harsh" and they also have a characteristic "bitterness".
As is apparent from the art, subjecting coffee beans to a hydrolysis reaction not only increases brew yields, but also alters or modifies at least some of the less desired characteristics of the less preferred or so-called low-grade varieties of coffee beans. As is generally accepted, hydrolysis is a reaction involving water and heat which cleaves chemical compounds. The hydrolysis reaction, however, provides beans which yield a brew which has significantly greater acidity than does a brew extracted from beans which merely have been roasted with hot gases. Roasting hydrolyzed beans with hot gases, however, tends to neutralize the increased acidity which makes extracts obtained from them more palatable, but at the same time, this roasting also decreases the yield increase resultant from the hydrolysis reaction.
A process which is said to produce more flavor and strength than prior conventionally roasted products is disclosed in U.S. Pat. No. 2,278,473. In that process, green coffee beans are placed in a chamber and subjected to an injection of steam at elevated pressure and temperature. After the steam treatment, the pressure is released quickly for exploding the beans for providing a cell-disrupted structure. The treated beans then are roasted with heat in an oven. It is taught that the moisture content of the steam treated beans should be below 20% to 25% for enabling the required explosion.
Another process for increasing the yield from green coffee beans is disclosed in U.S. Pat. No. 2,712,501 for obtaining an extract for preparing soluble coffee. After subjecting green beans to saturated steam in a closed vessel, the pressure is released slowly so that the treated coffee beans are not exploded or otherwise disintegrated. The beans then are extracted, but before dehydration to prepare the soluble coffee, the acidity of the extract is neutralized.
U.S. Pat. No. 3,572,235 discloses a process for enhancing flavor and aroma of certain coffees. Green beans first are contacted with steam under pressure under substantially non-oxidizing conditions to raise the moisture content of the beans to from about 12% to about 18% by weight for causing a hydrolysis reaction and a partial roasting of the green beans. Upon completion of the steam treatment, the pressure is released for causing a sudden swelling or puffing of the beans. The treated beans then are contacted with hot roasting gases under substantially oxidizing conditions.
U.S. Pat. No. 3,640,726 discloses a process in which green Robusta beans are placed in a pressure vessel and then, preferably, air is evacuated from the vessel by drawing a vacuum. The beans then are subjected to saturated steam under conditions described as essential for the beans to acquire a moisture content of from 15 weight percent to 35 weight percent and for partially roasting the beans. After steaming, the built-up pressure is released quickly. The treated beans then are subjected to roasting with circulating air at temperatures of at least about 190.degree. C.
Other methods proposed for increasing the soluble solids yield of coffees are those disclosed in U.S. Pat. Nos. 3,088,825 and 3,106,470 which are said to increase the soluble solids yield by from about 10% to about 50% as compared with coffee which is conventionally roasted. It is disclosed that these methods also improve the acidity and flavor characteristics of the coffees.
The '825 patent discloses a two part cycle which comprises first preheating green beans with a hot gas, which reduces the moisture content of the beans, and then contacting the preheated beans with steam under pressure in an enclosed vessel after which the pressure is released suddenly for obtaining puffing and expansion. The '470 patent discloses a three-part cycle comprising the preheating step and the steaming and expansion step, as in the '825 patent, and then a further step of roasting with hot air for a short time which is said to reduce acidity and improve flavor. Use of super-heated steam is advised in each patent so the moisture content of the treated beans is kept to a minimum, such as below 8% by weight, as indicated by the '825 patent.
Still further methods proposed by inventors associated with the assignee of the '825 and '470 patents, to improve the flavor and aroma of coffee varieties such as Robusta coffees, are those disclosed and referred to in U.S. Pat. Nos. 3,767,418, 4,540,591 and 4,671,964.
In the '418 patent it is taught to mix water with green coffee beans, and then to steam the mixture in a confined pressure vessel at an elevated temperature of from about 115.degree. C. to about 177.degree. C. and at a critical steam pressure of from at least about 3.5 kg/cm.sup.2 to below about 9.8 kg/cm.sup.2 for obtaining treated beans having a moisture content of from about 35% to 55% by weight, but preferably from 40% to 50% by weight, based upon the weight of the wet treated beans. The treated beans are released from the pressure vessel in a manner in which they do not experience substantial puffing or expansion and then are roasted with heated air, but preferably, prior to roasting, the beans are air dried to below 15% moisture by weight.
The '591 patent provides a method for roasting Robusta coffee and blending it with higher quality coffees in which green beans are placed in a pressure vessel such that there is void space for providing room for expansion during steaming under pressure. During processing, gas and condensed steam are vented from the vessel for removing what is said to be undesired gases, for minimizing loss of soluble solids and for reducing acids and sour notes in the treated beans. After steam treatment, the treated beans are roasted with hot gases or by the process of the afore-mentioned '825 patent.
The '964 patent, which makes reference to the '418 and '591 patents, seeks to provide an "efficient method" for upgrading the quality of poor quality beans. Green beans are treated with steam to preheat the beans to a temperature of from about 115.degree. C. to about 154.degree. C. for about 0.5 min. to about 3 mins., which raises the moisture content of the beans in addition to preheating them. The pre-treated beans then are moisturized with preheated water to a moisture level of from about 35% to about 45% by weight, and then the moisturized beans are steamed at a temperature of from about 115.degree. C. to about 154.degree. C. at a pressure of from about 1.4 kg/cm.sup.2 to about 4.9 kg/cm.sup.2 The beans then are roasted in a conventional manner, preferably after drying which lowers the moisture content.